(I suppose one could collect and use post stamps or coins too, but such a collection wouldn't last very long)
I know a funny story about this. I used to be a coin collector. Many years ago stores in the business were often "Stamp & Coin" dealers.
One of these wanted to get out of the stamp side of the business. This was before the internet.
He figured he would get stamp collectors mad at him by running an ad saying he would pay half of face value for uncanceled stamps. Non-collectors from all over brought in all kinds of postage stamps that had been tucked away in drawers or boxes. He even tried convincing people the stamps were still usable.
With his reputation on the line he ended up buying a lot of postage at half price. He used them to mail out his news letters.
And that is how my (excited) stamp collecting neighbor, at the time, got a canceled block of Civil War Veterans 50th anniversary commemorative stamps.
jtk
"A pessimist sees the difficulty in every opportunity; an optimist sees the opportunity in every difficulty."
- Sir Winston Churchill (1874-1965)